Argument
• Requires premises and conclusion
• Non-arguments : I don’t like chocolates;
Chocolates are makes you sick; I believe in
God
• Arguments: Chocolates are sweet- I do not
enjoy sweets- Therefore I don’t like
chocolates; I believe what my mother saysMy mother says that God exists- Thus I believe
in God
Valid Arguments
• Valid argument- Conclusion entailed from
premises [logically follows the premises]
• If P then Q exists. Q exists. So P
• Premises or conclusion don’t have to be true
• Deductive logic
Valid and Invalid Arguments
• Jessica is a man- Men have beards-Jessica has
a beard
• Jessica is a woman- Men are astronautsJessica is not an astronaut
• Andy is a boy- Boys are mammals-Andy is a
mammal
• Andy is cute man- Cute babies can be
naughty- Thus Andy is a naughty man
Valid and Invalid Arguments
• I believe what psychics say- A psychic said that
I would die yesterday- I believe I died
yesterday
• A psychic said that my dog is a ferret- I believe
him- I am dumb
• White tablecloths are not blue- My table cloth
is white- Thus it is not blue
• White skirts are not blue-My skirt is not blueThus it is white
Sound Arguments
•
•
•
•
Valid arguments +
True premises
As premises are true, conclusion is always true
If P then Q. Q. So P. P and Q is true, thus sound
argument
• Sound Argument: Jessica is a girl- Girls are human
beings- Jessica is a human being
• Unsound Argument: Jessica is a girl- Girls are prettyJessica is pretty
Sound and Unsound Arguments
• Jessica is a girl- Girls are human beings- Jessica
is a human being
• Jessica is a girl- Girls are pretty- Jessica is
pretty
• Cakes are food- Food can be eaten- Cakes can
be eaten
• Cakes are food- Food is always tasty- Cakes are
always tasty
Syllogism
• Form of an argument
• Proposition is proved or disproved in the
conclusion
• Major premise is universal, minor premise and
conclusion are particulars
Aristotelian Syllogism
• 3 categorical propostions
Major premise: All men are mortal.
Minor premise: All Greeks are men.
Conclusion:
All Greeks are mortal
Men are subject s, Greeks are predicate P and
mortals is the middle term
• Types of categoricals:
1. Universal Affirmative All S are P – S a P
2. Universal Negative- No S are P- S e P
3. Particular Affirmative- Some S are P- S i P
4. Particular Negative- Some S are not p- S o P
• Forms of syllogism
Major
Premise
M-P
P-M
M-P
P-M
Minor
Premise
S-M
S-M
M-S
M-S
Conclusion is always S-P
• 256 forms- 6 fallacies in each categories are
valid forms, some of them have an existential
fallacy i.e. an empty category
BARBARA
All men are
mortal. (MaP)
All Greeks are
men. (SaM)
All Greeks are
mortal. (SaP)
CAMESTROS
All horses have
hooves. (PaM)
No humans
have hooves.
(SeM)
Some humans
are not horses.
(SoP)
DARAPTI
All squares
are rectangles.
(MaP)
All squares
are rhombs.
(MaS)
Some rhombs
are rectangles.
(SiP)
DARII
All rabbits have
fur. (MaP)
Some pets are
rabbits. (SiM)
∴ Some pets
have fur. (SiP)
FESAPO
FRESISON
FALLACIES
• Fallacy is an error in argument or reasoning
• Formal fallacies can be spotted by invalidty in its
syllogistic form.
 Fallacies of Accident
• Verbal fallacies can be classified as:
 Fallacy of false cause
 Begging the Question
 Red Herring Fallacies
 Equivocation
 Informal fallacies
FALLACY OF ACCIDENT
• Post hoc [post hoc ergo poster hoc]: after this
therefore because of this
President Jones raised taxes, and then the rate
of violent crime went up. Jones is responsible
for the rise in crime.
• False dichotomy: either 2+2=5 or God exists.
God exists, thus 2+2 is not 5
RED HERRING FALLACIES
• Going off the tangent
Grading this exam on a curve would be the most
fair thing to do. After all, classes go more
smoothly when the students and the
professor are getting along well
RED HERRING FALLACIES
• Slippery Slope: slide down the bottom when
we stop halfway downhill
If I fail English 101, I won't be able to graduate.
If I don't graduate, I probably won't be able to
get a good job, and I may very well end up
doing temp work or flipping burgers for the
next year.
RED HERRING FALLACIES
• Ad hominem tu quoque [against someone-you
too] Failure to act consistently
Dia Mirza: I believe in ethical treatment of all
living beings; I’m a PETA member and I
endorse The Body Shop
Ms.X: The Body Shop may be vegan but it
owned by L’oreal which tests its products on
animals, thus you are cruel
RED HERRING FALLACIES
• Straw man fallacy: Wimpy version of
opponent’s argument and knock it down
Person A: Sunny days are good.
Person B: If all days were sunny, we'd never have
rain, and without rain, we'd have famine and
death. Therefore, you are wrong
BEGGING THE QUESTION
• Circular reasoning to prompt a question, the
answer is what you argue for
We know that God exists, because it says so in
the Bible. And we can trust the Bible on this
matter because it's the Word of God, and so
must be correct
INFORMAL FALLACIES
• Appeal to Ignorance
One cant prove that God doesn’t exist therefore
he exists
• Undistributed Middle/ Equivocation
Use of metaphor, middle term has more than
one implication
All polticians are snakes- Snakes have no legsPolticians have no legs
INFORMAL FALLACIES
• Appeal to authority: We should abolish the
death penalty. Many respected people, such
as actor Guy Handsome, have publicly stated
their opposition to it.
• Hasty generalization: My roommate said her
philosophy class was hard, and the one I'm in
is hard, too. All philosophy classes must be
hard
INFORMAL FALLACIES
• Missing the Point: The seriousness of a
punishment should match the seriousness of
the crime. Right now, the punishment for
drunk driving may simply be a fine. But drunk
driving is a very serious crime that can kill
innocent people. So the death penalty should
be the punishment for drunk driving
INFORMAL FALLACIES
• Ad populum [to the people]: Gay marriages
are just immoral because 70% of Americans
think so.
• Reductio ad absurdum
If P, then Q. But not-Q. So not-P
[Unbeatable computer game]